The invention concerns a method for the closed-loop speed control of an internal combustion engine-generator unit.
An internal combustion engine provided as a generator drive is usually delivered by the manufacturer to the end customer without the coupling and generator. The coupling and generator are installed at the end customer's facility. To guarantee a constant rated frequency for the current supply into the power supply system, the internal combustion engine is operated in a closed-loop speed control system. In this regard, the speed of the crankshaft is detected as a controlled variable and compared with a set speed, i.e., the reference input. The resulting control deviation is converted by a speed controller to a correcting variable for the internal combustion engine, for example, a set injection quantity.
Since definite data on the coupling characteristics and the moment of inertia of the generator are often unavailable to the manufacturer before the delivery of the internal combustion engine, the electronic control unit is often delivered with a robust set of controller parameters, i.e., the so-called standard set of parameters. One problem that exists in a closed-loop speed control system is that torsional vibrations, which are superimposed on the controlled variable, can be reinforced by the speed controller. Particularly critical are the low-frequency vibrations caused by the internal combustion engine, for example, torsional vibrations of the 0.5-th and 1st order. When the internal combustion engine-generator unit is started, the amplitudes of the torsional vibrations can become so large due to reinforcement by the speed controller that a limit speed is exceeded, and the internal combustion engine is shut off.
The problem of instability is countered by a speed filter in the feedback path of the closed-loop speed control system. As an additional measure, the controller parameters of the speed controller are changed, i.e., the proportional, integral, or differential component. A method of this type for switching the filter and a method for adapting the controller parameters is described, for example, in the unprepublished application DE 102 21 681.9. A problem associated with these methods is that they are not activated until unstable behavior of the internal combustion engine-generator unit already exists and has been detected.
A speed run-up ramp or its slope is stored in the aforesaid standard set of parameters for the starting process. To allow the fastest possible run-up, this parameter is set to a large value, e.g., 550 rpm/second. In the case of a generator with a large moment of inertia, a large deviation can develop between the set run-up ramp and the actual run-up ramp. This control deviation of the actual speed from the set speed causes a significant increase in the set injection quantity. In a diesel engine with a common-rail injection system, the significant increase in the set injection quantity promotes the formation of black smoke. The significant increase in the set injection quantity also causes nonoptimal determination of the injection start and the set rail pressure, since both of these values are computed from the set injection quantity. For the manufacturer of the internal combustion engine, this means that an on-site service technician must adapt the run-up ramp to the specific conditions. This is time-consuming and expensive.
A method described in the unprepublished application DE 102 52 399.1 deals with this problem of high adjustment expense. During the starting operation, an actual run-up ramp is determined from the actual speed. This actual run-up ramp is then set as the set run-up ramp. This method has proven effective in practice, but the optimum set run-up ramp becomes effective only starting with the second starting operation.